Acoustic tweezing at the nodes or antinodes of a heptagonal multi piezoelectric transducer cell

We present a novel device for acoustically manipulating or sonotweezing micron-scale elements. Such techniques, that allow the micro-manipulation of cells, particles or droplets by non-invasive means, are desired to facilitate biophysical or biological applications such as microarrays and tissue engineering. Non-invasive techniques exploiting the acoustic radiation force have been demonstrated for trapping, separating and moving particles. Most results to date describe acoustic trapping using geometrically fixed standing wave patterns. However, the concerted action of multiple transducers can be used to generate electronically controlled standing wave patterns. This paper investigates 2-D particle micro-manipulation in a closed system using two or three transducers. In such systems, wave reflections can be detrimental to performance hence the geometry of the device has a strong impact on the quality of the particle trapping and this is discussed. We will also demonstrate that acoustic trapping can occur at the nodes or antinodes depending on the properties of the particle suspended in the medium.